Brake actuator apparatus and method for actuating a brake

ABSTRACT

A brake actuating apparatus includes a force transmission element operable to transmit a brake actuating force and an abutment member moveable to abut the force transmission element. A piezo-electric device operable on expansion applies a force between the abutment member and the force transmission element to move the force transmission element in a direction of brake actuation. A support member moveable independently of the abutment member supports the force transmission element in the new position following expansion of the piezo-electric device.

The present invention relates to a brake actuator apparatus and method for actuating a brake.

A known vehicle braking system comprises a disc fixed for rotation with a wheel and a brake clamping mechanism comprising a tappet which is mechanically actuated to bring brake pads into contact with the disc and to apply a force between the pads and the disc to provide fictional braking.

Piezo-electric devices, which expand when energised by an electric voltage, are known for applying a mechanical actuating force over a short distance.

According to the present invention there is provided a brake actuating apparatus comprising:

-   -   a force transmission element operable to transmit a brake         actuating force;     -   an abutment member, moveable to abut the force transmission         element;     -   a piezo-electric device operable on expansion to apply a force         between the abutment member and the force transmission element         to move the force transmission element in a direction of brake         actuation; and     -   a support member moveable independently of the abutment member         to support the force transmission element in its new position         following expansion of the piezo-electric device.

Preferably the piezo-electric device is fixed for movement with the first abutment member. Alternatively, the piezo-electric device may be fixed for movement with the force transmission element.

Preferably, the apparatus further comprises a body member, and the abutment member has a threaded portion in threaded engagement with the body member so as to be moveable by relative rotation between the abutment member and the body member.

Preferably, the support member has a threaded portion in threaded engagement with a further body member of the apparatus, so as to be axially moveable by relative rotation between the support member and the further body member.

Conveniently, the abutment member and support member are rotatable by respective rotation means. Alternatively, the body member and further body member are rotatable by respective rotation means

Preferably, the rotation means are electric motors.

Preferably, for releasing the brake, the support device is arranged to support the force transmission element for movement of the abutment member, with the piezoelectric device contracted, to a position wherein expansion of the piezo electric device causes the abutment member to abut the force transmission element, whereby the support member is moveable to a position wherein contraction of the piezoelectric device allows the force transmission element to move into abutment with the support member.

According to a further aspect of the present invention, there is provided a method for actuating a brake comprising the steps of:

-   -   a) moving an abutment member into abutment with a force         transmission element operable for transmitting a brake actuating         force;     -   b) expanding a piezo-electric device to apply a force between         the abutment member and the force transmission member to move         the force transmission element in a diction of brake actuation;     -   c) moving a support member into abutment with the force         transmission element so as to support the force transmission         element in its new position;     -   d) contracting the piezoelectric device; and     -   e) repeating steps a to d for as many times as required to         actuate the brake.

Preferably, the method further comprises the following steps for releasing the brake:

-   -   f) with the force transmission element supported by the support         member and the piezo-electric device contracted, moving the         abutment member out of abutment with the force transmission         element;     -   g) expanding the piezoelectric device to cause the abutment         member to abut the force transmission element;     -   h) moving the support member away from the force transmission         element;     -   i) contracting the piezo electric device to cause the support         member to support the force transmission element; and     -   j) repeating steps f to i for as many times as required to         release the brake.

It is an advantage of the apparatus and method herein described that although the distance that the piezo-electric device moves is small, by repeatedly expanding and contracting the device, and moving the abutment member and support member to abut the force transmission element the piezo-electric device may be used to provide a substantially larger movement to the force transmission element.

Furthermore, because a braking mechanism has a degree of elasticity in its structure, a degree of elastic deformation has to be taken up by the structure before the force applied by the actuating means is transmitted to the brake pads. With the present invention a piezo-electric device may be used to move the force transmission element beyond the elastic deformation of the structure and to apply the braking force.

A further advantage is that the same apparatus may also be used to release the brake.

An embodiment of the invention will now be described by way of example, with reference to the accompanying drawings in which:

FIGS. 1 a to 1 e show the stages in the operation of a brake actuator to apply an actuating force;

FIGS. 2 a to 2 d show the stages in the operation of the actuator of FIGS. 1 a to 1 e for releasing the brake.

Referring to FIG. 1 a, an actuator 5 for actuating a brake comprises an abutment member in the form of a pin 10 arranged on an axis of the actuator 5. The pin 10 has a threaded portion 11 in threaded engagement with an associated first body member 12 of a vehicle brake mechanism. The first body member 12 is axially fixed with respect to the brake mechanism. A piezo-electric device 14, comprising at least one piezo-electric element, is fixed to the pin 10 and is operable to be expanded by application of an electric voltage. The pin 10 abuts a force transmission element in the form of a tappet 16 for transmitting an applied actuating force in an axial direction. The tappet 16 forms part of a clamping mechanism for exerting a clamping force on a pair of brake pads in response to application of the brake.

Also shown in FIG. 1 is a support member in the form of a sleeve 18 having a threaded portion 19 in threaded engagement with an associated second body member 20 of the brake mechanism. The second body member 20 is axially fixed with respect to the brake mechanism: The sleeve 18 is substantially coaxial with and surrounds the pin 10. The sleeve 18 abuts the tappet 16 to support it.

The threaded engagements 11, 19 of the pin 10 and sleeve 18 provide axial movement by relative rotation between the pin 10 and sleeve 18 and their respective associated body members 12, 20. Rotational motion is provided to the pin 10 or the sleeve 18 by associated electric motors (not shown). Alternatively, rotational motion may be provided to the first and second body members 12, 20.

It will be appreciated that the piezo-electric device 14 does not need to directly abut the tappet 16 (as shown in FIGS. 1 a to 1 e and 2 a to 2 e), but may be situated at any position along the length of the pin 10 so that expansion of the piezoelectric device 14 causes the pin 10 to abut the tappet 16 and to apply a force in the axial direction. Alternatively, the piezo-electric device 14 could be attached to the tappet 16.

Referring to FIG. 1 b, in the first stage of actuation of the brake the piezo-electric element 14 is expanded by application of the electric voltage so as to apply a force to the tappet 16 and to move tappet 16 in the axial direction. Tappet 16 moves out of contact with the sleeve 18.

In the second stage, shown in FIG. 1 c, the sleeve 18 is rotated so as to move axially to abut the tappet 16.

In the third stage, shown in FIG. 1 d, the piezoelectric element 14 is contracted by removal of the electric voltage, moving the pin 10 out of contact with the tappet 16.

In the fourth stage, shown in FIG. 1 e, the pin 10 is rotated so as to move axially to abut the tappet 16. The actuator 5 is now in the same configuration as in FIG. 1 a, although the tappet 16, pin 10, and sleeve 18 have been moved in the axial direction.

The stages shown in FIGS. 1 a to 1 e are then repeated as many times as required to take up the elastic deformation of the brake mechanism and to apply the required braking force to the brake.

Thus, although only a small movement of the tappet 16 can be effected by a single expansion of the piezoelectric device 14, the brake can be actuated by repeated expansion and contraction of the piezoelectric device 14.

Referring to FIG. 2 a, in the first stage of releasing the brake the pin 10 is rotated so as to move a first predetermined distance axially away from the tappet 16.

The first predetermined distance is set such that in the second stage, shown in FIG. 2 b, the piezo-electric device 14 is expanded so as to abut the tappet 16 and move it just clear of the sleeve 18.

In the third stage, shown in FIG. 2 c, the sleeve 18 is rotated so as to move a second predetermined distance axially away from the tappet 16.

The second predetermined distance is set such that in the fourth stage, shown in FIG. 2 d, the sleeve 18 is in a position whereby, when the piezoelectric element 14 is contracted, the tappet 16 moves axially to just abut the sleeve 18 before the piezoelectric element 14 has fully contracted.

The stages shown in FIGS. 2 a to 2 d are repeated to further release the brake. 

1. A brake actuating apparatus comprising: a force transmission element that transmits a brake actuating force; an abutment member that selectively abuts and disengages the force transmission element; a piezo-electric device that is expandable to apply a force between the abutment member and the force transmission element to move the force transmission element in a direction of brake actuation; and a support member moveable independently of the abutment member to support the force transmission element stationary in a new position following expansion of the piezo-electric device.
 2. The brake actuating apparatus according to claim 1 wherein the piezo-electric device is attached to the abutment member.
 3. The brake actuating apparatus according to claim 1 wherein the piezo-electric device is attached to the force transmission element.
 4. The brake actuating apparatus according to claim 1 further including a first body member, and the abutment member has a threaded portion in threaded engagement with the first body member and is moveable by relative rotation between the abutment member and the first body member.
 5. The brake actuating apparatus according to claim 1 further including a second body member, and the support member includes a threaded portion in threaded engagement with the second body member and is axially moveable by relative rotation between the support member and the second body member.
 6. The brake actuating apparatus according to claim 1 wherein at least one of the abutment member and the support member is rotatable by a rotation device.
 7. The brake actuating apparatus according to claim 1 further including a first body member and a second body member, and the abutment member has a first threaded portion in threaded engagement with the first body member and the abutment member is moveable by relative rotation between the abutment member and the first body member, and the support member has a second threaded portion in threaded engagement with the second body member and the support member is moveable by relative rotation between the support member and the second body member, wherein at least one of the first body member and the second body member is rotatable by a rotation device.
 8. The brake actuating apparatus according to claim 6 wherein the rotation device is an electric motor.
 9. The brake actuating apparatus according to claim 1 wherein the support member supports the force transmission element for movement of the abutment member, with the piezo-electric device contracted, to an expanded position wherein expansion of the piezoelectric device causes the abutment member to abut the force transmission element, and the support member is moveable to a contraction position wherein contraction of the piezo-electric device allows the force transmission element to move into abutment with the support member.
 10. A method for actuating a brake comprising the steps of: a) moving an abutment member into abutment with a force transmission element operable for transmitting a brake actuating force; b) expanding a piezo-electric device to apply a force between the abutment member and the force transmission element to move the force transmission element in a direction of brake actuation into a new position; c) moving a support member into abutment with the force transmission element to support the force transmission element in said new position; d) contracting the piezo-electric device; and e) repeating steps a) to d) to actuate the brake.
 11. The method for actuating a brake according to claim 10 further comprising the steps of: f) moving the abutment member out of abutment with the force transmission element while the force transmission element is supported by the support member and the piezo-electric device is contracted; g) expanding the piezo-electric device to abut the abutment member on the force transmission element; h) moving the support member away from the force transmission element; i) contracting the piezo-electric device to cause the support member to support the force transmission element; and j) repeating steps f) to i) to release the brake.
 12. (CANCELLED)
 13. The brake actuating apparatus according to claim 7 wherein the rotation device is an electric motor. 